\section{Introduction}\label{sec:intro}
Considering the fact: TV took 13 years to reach 50 million users, Internet took 4 years to reach that number. While for facebook, it only took less than 9 months, social networking sites undoubtly can be called a revolution. 

Fortruantly It offers identity and realationship maintainance as basis. SW distinguished itself from traditional web services by providing various Social Network Services(SNS) based on this basis. Emerging and wide-spreading of SNS such as microblogging and social-bookmark. Moreover some traditional internet services became socialized by integrating social network features. Those changes turned out a new wave of development on internet. Although SW became popular in unprecedented speed, it's sill considered in its novel stage. In reality, there are hurdles keeping SW from reaching its promised potential power: open collective intellegence\cite{1012809}.

Social networking site also changed our view on interenet. Rather than merely an information media, internet lets people socialize or interact with each other. The concept of Social Web that researches expected as the future of networking,    
\para{What is social web and what is not?} As a socialology concept, social network means a social structure composeted by individuals and 
relationships within them. An online social network or virtual community, however, means a internet-based communitaion and informations system of social network. 

Arguably virtual communities may emerge before internet. Retrospectively the first communities without propinquity appeared in 17th centrury. The Royal Society of London formed a community through letrer exchanging. After that As the development of communication, various new form of communities became less and less geographically binded and more and more based on weak ties between strangers. 

The idea of social network is both old and new. Alghouth it is a comman phenomenon existing in every human interaction, when we talk about Social Web, in this paper, we intend to focus on online social networking sites, which is also called ``online social networks'' or ``virtual communities''. 

According to Weyer's definition, social networking sites is an autonomous form of coodination of interactions whose essence is the trust cooperation of autonomouse, but interdependent agents who cooperate for a limited time, considering their partners' interests, because they can thus fulfil their individual goals better than through non-coordinated activities. Based on that online social networks has four nominant characters: weak ties, no presistant connection, trust based on interdependent, autonomous collaboration.

Before social networking sites, relationships and personal profiles
 information information  enterprise group 

Although social networking sites may various in scale and type of ties (e.g., Alumni social networking websites may more rely on solid and strong relationships within classmates), Social network distinguished itself from other collabration platforms ware which is built on strong relationships with organizations. 

On the other hand, it's eclastic to set a hard line between social web and it's precedent online communities. M
 
 Within them, BBS and Newgroup have similar features in certain usages. 

social web is not designed, 
Until Social Web, specialized utilites within the platform have not been specialised. 

Web 2.0 

We also draw heavly on the work of social networking analysing -- measure paper. 
Our paper offer something new: